Pyrolysis of methane



Nov. 24, 1936. H. M. SMITH ET AL PYROLYSIS OF METHANE Filed April 26,1934 FlGURE 1 FIGURE 2 fl m' lNVEN ORS A ORNEY t atenteei Nova 2d, lgddsarra tried e htthtti rrnoarsre or nmrnann Harold M. Smith, PeterGrandone, and Harry 'E. Rail, hartlesvillle, (thin Application npniac,ran, seen-ac, teaser zfllaima, (crate-ice) (Granted micathe act at Marcha, rats, at

amended April 3%, 1928; 3% (G. W57) This invention described herein maybe manufactured and used by or for the Government for governmentalpurposes, without the payment to usv of any royalty thereon.

This invention relates to the pyrolytic synthesis oil (benzene)investigators have, been handicapped in obtaining their objectivethrough lack of sufilcient information as to conditions necessary forthe most eflicient treatment. This deficiency arises especially throughlack of data concerning the decomposition rates of the hydrocarbongases. Methane has been particularly neglected in this regard, andthermal decompositions designed to produce light oil (benzene), havebeen conducted largely on a trial and error basis. We, have conducted asystematic pyrolyti'c study of methane and have ascertained someIof theoperating conditions necessary "when this gas is processed to producelight oil (benzene).

One object therefore pf this invention is to provide a method for theproduction or light-oil (benzene) from methane. I

When natural gas hydrocarbons are subjected to the action of heat thesimple hydrocarbons are split and free radicals are formed. These "freeradicals very quickly recombine, in numerous new and differentcombinations, and these new compounds are also subject to condensationand v polymerization reactions so that there finally results from thethermal decomposition a number of different products such as hydrogen,acetylene, ethylene, benzene, naphthalene, anthracene,

pyrene and increasingly heavier compounds an til the final degradationproduct, carbon, is obtained. Some of the products are what may betermed primary reaction products in that they are the simplest productsthat can be isolated in a stable condition; while other products aredesignated as secondary in that they may be assumed to proceed from thepolymerization and condensation reactions of the primary products.Hydrogen, acetylene, and ethylene, are examples of the primary productsand benzene, naphthalene, and the remainder of the heavy compounds areexamples of secondary products.

Since .the object of this invention is the produc:

tion of one of the secondary products it is apparent that the timefactor is of great im-, portance. In other words if a maximum productionof light-oil (benzene) is to be obtained the series of reactions startedby the application of heat must proceed far enough so that the pri maryproducts are converted to a maximum amount of light-oil (benzene), butthese reac-- tions must be stopped before the production oi heavyhydrocarbons is increased at the expense of the light-oil (benzene).

We have carried out numerous experiments to determine the decompositionrates for methane at dififerent temperatures. As a result of theseexperiments we have found a linear relationship between the specificdecomposition rate K, expressed in reciprocal seconds, and thereciprocal of the temperature in degrees Kelvin. This relationship isillustrated in Figure 1, where the logarithm of K is plotted against thereciprocal of the temperature in degrees Kelvin, and may be expressed asfollows:

logmK= reacts In using this equation it is essential that I rep resentthe average'temperature or the gases in the cracking zone as closely asit can be determined. v This equation is valid over the cracking rangeoi1000 C. to 1200 0.

We have also discovered that when methane is reacting according to theabove equation that the maximum yields of light-oil (benzene) at a giventemperature are obtained when only sumcient time is allowed forapproximately 25 percent by weight of the methane to be decomposed. Inaccordance with these discoveries when methane is processed to producethe maximum amount of light-oil (benzene) at a certain term perature atatmospheric pressure, the time c which a given particle of gas shouldremain in the reaction tube is given by the iollowing equation whichresults from combining these two diecoveries and expressing them in thelogaritmc form:

- ia,s25 I IOQpfl- I wherein the contact time in-seconds is representedby the Greek letter theta. I

l or example, if it is desired to determine the contact time necessaryto process methane tor .maximurn light-oil (benzene) yield at 115W thenaccording to the above equation, since llb C.=l l23 K, we have then ' d=.ll-fit second Coming now to a more detaileddescription of the process,reference is made to Figure 2 which is ing chamber 3. This chamber mayconsist of a single tube, or of several lengths of tubing arranged inparallel or even as a coil, but regardless of its arrangement the gasmust enter at 5 such a rate that it will remain in the heated Inconclusion the gas containing the light-oil (benzene) vapors may now besubjected to appropriate scrubbing and recovery methods l for which theusual commercial equipment is suit- 20 able. In fact the entire processmay be carried out in equipment that conforms to the usual commercialpractices, the only criterion being that the cracking unit have theproper volume to provide a contact time in accord: :ice with the 26previously cited equation.

Having described our invention, what we claim as 'new and wish to securebyLetters Patent is: 1. A process for the pyrolytic conversion ofmethane into benzene, consisting in limiting the methane decompositionto approximately 25 percent by weight for any temperature within thetemperature range of 1000 C.1200 C. by passing the gas through areaction tube at any temperature between 1000 C.-1200 C. at atmosphericpressure and at a time interval expressed by the formula log 0 15.0967

wherein the contact time in seconds is represented by the Greek lettertheta.

HAROLD M. SMITH. PETER GRANDONE. HARRY '1. BALL.

